Meisetz and the birth of the KRAB motif

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Abstract
The largest family of transcription factors in mammals is of Cys2His2 zinc finger-proteins, each with an NH2-terminal KRAB motif. Extensive expansions of this family have occurred in separate mammalian lineages, with ∼400 such genes known in the human genome. Despite their widespread occurrence, the evolutionary provenance of the KRAB motif is unclear since previously it has not been found outside of the tetrapod vertebrates. Here, we show that homologues of the histone methyltransferase Meisetz are present within the sea urchin (Strongylocentrotus purpuratus) genome. Sea urchin and mammalian Meisetz sequences each contain an N-terminal KRAB motif, which thereby establishes an early origin of the KRAB motif prior to the divergence of echinoderm and chordate lineages. Finally, we present evidence that KRAB motifs derive from a novel family of KRI (KRAB Interior) motifs that were present in the last common ancestor of animals, plants and fungi. Contact:chris.ponting@anat.ox.ac.uk Supplementary information: Supplementary data for this article are available at Bioinformatics online.